Stabilisation of intertidal cobbles and gravels by Goniastrea aspera: an analogue for substrate colonisation during marine transgressions?

There is a widespread perception that coral larvae require stable (lithified) rock substrates to settle during reef initiation, and that these substrates are typically carbonate. However, reef core data show that reef establishment can also occur directly above a wide range of unlithified, non-carbonate sediment substrates, including relict alluvial sands and gravels. The mechanisms by which these lithic substrates are colonised and stabilised are not, however, well documented. Here, we describe such processes from an intertidal setting on the inner-shelf of the Great Barrier Reef, in a setting directly analogous to that which would have existed around many inner-shelf high islands during the post-glacial marine transgression when mid-Holocene reef initiation was taking place